Recently, a fuel cell motorcycle which is a motorcycle having a solid polymer fuel cell mounted therein is being developed. The fuel cell motorcycle is run by rotating a motor with an electric power generated by the solid polymer fuel cell and thus driving a driving wheel. The solid polymer fuel cell is a device which generates electricity by reacting hydrogen supplied to a fuel electrode with air (oxygen) supplied to an air electrode (oxygen electrode) via a solid polymer electrolyte film. Such a fuel cell motorcycle is described in Patent Documents 1 and 2.
Also, the solid polymer fuel cell includes water-cooled and air-cooled types depending on a cooling method of heat generated during reaction. In general, the water-cooled type fuel cell has a compressor, a cooling water duct, a radiator, a humidifier and the like as a cooling mechanism and realizes cooling by these instruments. Contrarily, the air-cooled type fuel cell can realize cooling while eliminating the instruments. If an electric power generated by the fuel cell is 20 kW or less, a volume of a cooling mechanism in the air-cooled type is smaller than that in the water-cooled type. Accordingly, in small vehicles such as fuel cell motorcycles, the air-cooled type fuel cell is commonly mounted therein.
Further, in order to allow the solid polymer fuel cell to continuously generate electricity, hydrogen is converted to hydrogen ion and then the hydrogen ion has to penetrate the solid polymer electrolyte film. Therefore, the electrolyte film needs to be wetted. In the water-cooled type fuel cell, air to be supplied to the fuel cell is humidified by the humidifier, thereby maintaining a wet state of the electrolyte film. On the other hand, in the air-cooled type fuel cell, humidification of the electrolyte film is performed using moisture generated by reaction therein. Specifically, when the electrolyte film of the air-cooled type fuel cell is humidified, an inlet and an outlet of a path through which air flows are closed by shutters or the like and a fan creating a flow of the air is stopped. Thus, the vapor and the reaction water are stayed in the electrolyte film, thereby humidifying the electrolyte film.    Patent Document 1: Japanese Patent Application Publication No. 2009-043687A    Patent Document 2: Japanese Patent Application Publication No. 2004-296339A
The fuel cell motorcycle having the air-cooled type solid polymer fuel cell mounted therein has the following problems.
In other words, upon cornering of the motorcycle, an inclination and a speed of a vehicle body are adjusted so that the centrifugal force and the gravity exerted on the vehicle body are balanced with each other, thereby balancing the vehicle body and thus stabilizing running thereof. For example, when a lateral inclination of the vehicle body is excessively increased upon cornering, an accelerator (throttle) is opened to increase a speed, so that the centrifugal force exerted on the vehicle body is increased and thus the inclination of the vehicle body is decreased, thereby balancing the vehicle body. Accordingly, in the motorcycle, a state where an output of the motor can be sufficiently increased instantly in response to opening of the accelerator by a driver upon cornering has to be ensured.
However, in the air-cooled type solid polymer fuel cell, as described above, humidification of the electrolyte film is performed by blocking air to be supplied to the fuel cell. Accordingly, during performing of such a humidification treatment, the fuel cell becomes a state where generation of electricity is almost stopped, and accordingly an output of the motor using an electric power from the fuel cell is inevitably reduced. Therefore, in the fuel cell motorcycle, if the humidification treatment is performed upon cornering, a state where an output of the motor cannot be sufficiently increased even when the accelerator is opened is likely to be occurred. As a result, it is difficult to balance the vehicle body with only an electric power from the fuel cell upon cornering, thereby damaging stability of running.
Meanwhile, in the fuel cell motorcycle, the motor can be also driven with an electric power from the secondary battery, but in general, a capacity of the secondary battery in the fuel cell motorcycle is not large. Accordingly, when the motor is driven with an electric power from the secondary battery, a magnitude or duration of an output of the motor is limed as compared with a case where the motor is driven with an electric power from the fuel cell. Therefore, it is difficult to fully leave stability of running upon cornering to driving of the motor with an electric power supplied from the secondary battery.
The above problems can be also occurred in situations where it is important to balance the vehicle body by operation of the accelerator, other than upon cornering.